Reproductive dysfunction

Abstract

• Polycystic ovary syndrome (PCOS) is classically characterised by ovarian dysfunction (oligomenorrhoea, anovulation and infertility), androgen excess (hirsutism and acne), obesity, and morphological abnormalities of the ovaries (cystic enlargement and stromal expansion).
• More recently, insulin resistance has been found to be common in PCOS, along with an increased prevalence of other features of the "metabolic syndrome", namely glucose intolerance, type 2 diabetes mellitus, and hyperlipidaemia.
• Hyperinsulinaemia is likely to contribute to the disordered ovarian function and androgen excess of PCOS.
• Reducing insulin resistance by lifestyle modifications such as diet and exercise improves endocrine and menstrual function in PCOS. These lifestyle modifications are the best initial means of improving insulin resistance.
• Metformin, an oral hypoglycaemic agent that increases insulin sensitivity, has been shown to reduce serum concentrations of insulin and androgens, to reduce hirsutism, and to improve ovulation rates. The effect of metformin alone on fertility rates is unknown. Some studies suggest that metformin will reduce total body weight to a small extent, but with a predominant effect on visceral adipose reduction.
• The effects of metformin on lipid abnormalities, hypertension or premature vascular disease are unknown, but the relative safety, moderate cost, and efficacy in reducing insulin resistance suggest that metformin may prove to be of benefit in combating these components of the "metabolic" syndrome in PCOS. Further properly planned randomised controlled trials are required.

As there is some phenotypic overlap between patients with congenital adrenal hyperplasia or Cushing's syndrome and those with PCOS, the work-up should include consideration of these differential diagnoses. The prevalence of PCOS in premenopausal women is said to be 6%-10%.¹

PCOS and insulin resistance

However, in women with PCOS the ovary does not appear to be resistant to insulin when studied in vitro. Insulin action in the ovary is mediated via the insulin receptor rather than the type 1 insulin-like growth factor (IGF) receptor, which binds IGF-I with high affinity and insulin with low affinity. Insulin increases ovarian androgen production and may thereby impair ovulation,⁴ suggesting that hyperinsulinaemia may be pathogenetically important in PCOS.

Strategies that reduce insulin resistance, such as weight loss, diet and exercise, have been shown to improve hyperinsulinaemia, menstrual abnormalities, and ovulation rates.⁵ This forms the basis for the potential use of metformin to treat the raised androgen concentrations and menstrual disturbances in PCOS (see Box 2). There is also emerging support for the use of other insulin-sensitising agents, such as thiazolidenediones,⁶ but that is beyond the scope of this review.

Metformins

Published studies on metformin in PCOS

The non-randomised studies found:

Effects on fasting insulin levels and insulin resistance in PCOS: Most studies claim some reduction in fasting and glucose-stimulated insulin levels as well as improvements in insulin sensitivity. However, others fail to confirm these observations. There is no apparent explanation on the basis of doses used, but the degree of obesity is important in the response.

Effects on androgens and sex-hormone-binding globulin: Most studies show beneficial effects on free testosterone and sex-hormone-binding globulin levels. However, this is not supported by other studies which are similar in design.

Effects on menstruation, ovulation and pregnancy: Most publications do not deal with clinical outcomes. Those that do indicate improvement in spontaneous menstruation in 20%-50% of women. Some women became pregnant.

There were only five randomised trials comparing metformin with placebo in PCOS to July 1999.^7-10,18 A single-blind crossover study showed no difference in insulin resistance between the placebo and metformin arms of the trial after treatment.⁷ Another study was unable to show any benefit of metformin over placebo when both were used in combination with diet.⁸ Neither of these two studies addressed clinical reproductive outcomes. Of the remaining randomised trials, two dealt with hormonal outcomes in obese and non-obese women with PCOS, and showed an improvement in insulin secretion, luteinising-hormone- stimulated 17-hydroxyprogesterone secretion, decreased levels of luteinising hormone and free testosterone, and an increased level of sex-hormone-binding globulin with metformin therapy.^9,18 The third looked at the effects of metformin with or without clomiphene citrate on ovulation.¹⁰ Sixty-one women with PCOS were randomly allocated to treatment with metformin or placebo, with 34% and 4%, respectively, ovulating after taking 1500 mg daily of metformin or placebo. Of those who did not ovulate, 90% in the metformin group responded to the addition of clomiphene citrate, compared with only 4% in the placebo group. Pregnancy was not an outcome measure in this study and few of the other studies reported pregnancies.

During the preparation of this review (through to January 2001), we became aware of an additional 12 interventional (but not placebo-controlled) studies of metformin in PCOS;^21-31 these studies reinforce the conclusions above. One important study randomly allocated women to therapy with metformin or conventional therapy for normalising menstrual activity and reducing androgen excess (ethinyl oestradiol plus cyproterone acetate).³⁰ This study showed reductions in body weight, insulin levels and androgens with metformin, but an increase in glucose intolerance with the conventional therapy.

Two important randomised, double-blind, placebo-controlled trials of metformin therapy in women with PCOS have recently been published.^32,33 In one, 23 women with PCOS randomly allocated to treatment with either placebo or metformin (500 mg three times daily) for six months showed significant benefits in menstrual pattern, ovulation rate, insulin sensitivity, serum free testosterone levels, and gonadotropin-releasing-hormone-stimulated 17-hydroxyprogesterone levels without changes in body weight.³² Almost 50% of the women involved developed ovulatory cycles during an open-label, long-term extension of the study. In the other, 20 women with obesity and PCOS and 20 with obesity only were randomly assigned to either placebo or metformin therapy (850 mg twice daily) for six months. Metformin reduced visceral fat mass and improved glucose-stimulated insulin levels, hirsutism and menstrual pattern in those with PCOS. Two studies now show that metformin decreases hirsutism.^30,33

What should doctors do?

The literature supports a trial of metformin in patients with anovulation, androgen excess and vascular risk factors, as these abnormalities may be reduced. However, the long-term effects of treatment with metformin on vascular risk factors, morbidity and mortality are unknown. Clinically relevant end-points to follow may include fasting serum glucose levels (with or without tests for oral glucose tolerance and fasting plasma insulin level), fasting serum levels of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol, blood pressure, serum testosterone level and hirsutism and acne, and menstrual pattern and fertility. Side effects of metformin (which include diarrhoea and vitamin B₁₂ malabsorption) may limit compliance in some patients. Lactic acidosis is a rare but serious side effect in diabetes, but has not been described in PCOS.

Given the present lack of long-term safety data and demonstrable efficacy in a large number of patients, we recommend that metformin use be supervised by an endocrinologist or physician with expertise in the area. Ideally, further research should be encouraged so that outcomes can be scrutinised and regulatory issues can be carefully addressed.

A summary of recommendations for the use of metformin in PCOS is shown in Box 3.

References

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Authors' details

Prince of Wales Hospital, Randwick, and the Children's Hospital, Sydney, NSW.
Warren J Kidson, MB BS, FRACP, Visiting Medical Officer; and Visiting Endocrinologist, Royal Hospital for Women, Paddington, NSW.

Metabolic Research Unit, Department of Medicine, University of Queensland, and Department of Diabetes and Endocrinology, Princess Alexandra Hospital, Brisbane, QLD.
Ross C Cuneo, FRACP, PhD, Endocrinologist.

Department of Endocrinology and Paediatrics, The Royal Children's Hospital, Melbourne, VIC.
Margaret R Zacharin, MB BS, FRACP, Endocrinologist.

Reprints will not be available from the authors.
Correspondence: Associate Professor R C Cuneo, Department of Medicine, Princess Alexandra Hospital, Brisbane, QLD 4102.

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